rsmith added inline comments.
================
Comment at: lib/AST/ItaniumMangle.cpp:272-299
@@ -265,1 +271,30 @@
+ // abi_tag is a gcc attribute, taking one or more strings called "tags".
+ //
+ // The goal is to annotate against which version of a library an object was
+ // build and to be able to provide backwards compatibility ("dual abi").
+ //
+ // For this the emitted mangled names have to be different, while you don't
+ // want the user to have to use different names in the source.
+ //
+ // The abi_tag can be present on Struct, Var and Function declarations as
+ // "explicit" tag, and on inline Namespace as "implicit" tag. Explicit tags
+ // are always emitted after the unqualified name, and (implicit) tags on
+ // namespace are not.
+ //
+ // For functions and variables there is a set of "implicitly available"
+ // tags. These tags are: all tags from the namespace/structs the name is
+ // embedded in, all tags from any template arguments of the name, and, for
+ // functions, alls tags used anywhere in the <bare-function-type> (i.e.
+ // parameters and sometimes the return type).
+ //
+ // For functions this is basically the list of all tags from the signature
+ // without the unqualified name and usually without the return type of the
+ // function. In `operator Type()` Type is NOT part of that list, as it is
+ // part of the unqualified name!
+ //
+ // Now all tags from the function return type/variable type which are not
+ // "implicitly available" must be added to the explicit list of tags, and
+ // are emitted after the unqualified name.
+ //
+ // Example:
----------------
Just reference the documentation for most of this, you don't need to duplicate
so much of the description here.
================
Comment at: lib/AST/ItaniumMangle.cpp:275
@@ +274,3 @@
+ // The goal is to annotate against which version of a library an object was
+ // build and to be able to provide backwards compatibility ("dual abi").
+ //
----------------
build -> built
================
Comment at: lib/AST/ItaniumMangle.cpp:321-323
@@ +320,5 @@
+ // track.
+ //
+ // FIXME: how to handle substituted names? They should add the tags used in
+ // the substitution to the list of available tags.
+ class AbiTagState final {
----------------
Do we need to? IIUC, the only time we need this list is when determining the
set of "available" tags for a function declaration with a tagged return type,
and in that case, a tag can only be available from a substitution if it's also
available from the target of that substitution (right?).
================
Comment at: lib/AST/ItaniumMangle.cpp:326-328
@@ +325,5 @@
+ //! All abi tags used implicitly or explicitly
+ std::set<StringRef> UsedAbiTags;
+ //! All explicit abi tags (i.e. not from namespace)
+ std::set<StringRef> EmittedAbiTags;
+
----------------
It seems unnecessarily expensive to hold these as `std::set`s.
================
Comment at: lib/AST/ItaniumMangle.cpp:348-361
@@ +347,16 @@
+
+ void pop() {
+ if (!LinkActive)
+ return;
+
+ assert(LinkHead == this &&
+ "abi tag link head must point to us on destruction");
+ LinkActive = false;
+ if (Parent) {
+ Parent->UsedAbiTags.insert(UsedAbiTags.begin(), UsedAbiTags.end());
+ Parent->EmittedAbiTags.insert(EmittedAbiTags.begin(),
+ EmittedAbiTags.end());
+ }
+ LinkHead = Parent;
+ }
+
----------------
Why do we need a stack of these? It seems like we only need one set of
available tags for the complete mangling process (it should only be used once
at the top level).
http://reviews.llvm.org/D18035
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